The long term interest of this laboratory lies in understanding the control of gene activity. In depth studies of bacteria and their viruses have long revealed the importance of specific interactions between segments of the chromosome and controlling proteins in governing whether a given gene is transcribed and translated. For some time we have devoted our efforts to studying the mechanism of gene regulation in the L-arabinose system of E. coli. This system has provided us with the first example of positive control, and the genetic and biochemical analyses that followed have revealed an intricate pattern of regulation, involving both positive and negative mechanisms. Genes encoding the three enzymes required for arabinose utilization form the araBAD operon, the expression of which is controlled both positively and negatively by the neighboring araC gene. Transcriptions of araBAD and araC are initiated in the region between araBAD and araC, and are divergent. The araC gene is autoregulated in a negatively manner, and is also positively controlled by the c'AMP system. Recently we have established the functional domains within the molecular structure of the araBAD and araC promoters and controlling sites, correcting the view for araC autoregulation then current. Our proposed research plans are: (1) to continue an effort, already initiated, to carry out a detailed genetic dissection of the araBAD promoter and its regulatory region DNA, by sequencing both directly-selected and in vitro mutagen-induced mutations in this region, and then examining their functional alterations in their responses to RNA polymerase and activator protein in the reactions of transcription initiation, (2) to investigate the mechanism of negative control of this promoter by araC: seeking a more concise positional definition of the control site DNA thru in vitro deletion analysis, and testing the current model by direct methods, and (3) to analyse the structure and function of the araC gene by isolating and characterizing amino acid substituted proteins to determine whether the various functions associated with the araC protein are mutationally separable, and, if possible, to identify specific amino acids involved with each function.